1. Field of the Invention
The present invention relates to computer aided design (CAD) used to design integrated circuits, and more specifically to a method and apparatus for measuring current density parameters on signal leads of an integrated circuit.
2. Related Art
Integrated circuits generally contain several components such as flip-flops, logic gates, multiplexors, and comparators. Components in an integrated circuit are interconnected using medium such as metal wires, which are generally referred to as signal leads. Thus, a signal lead is typically designed to carry/transfer a signal from a component (hereafter ‘driver cell’) to another component (hereafter ‘load cell’). The signal, when transferred, is characterized by several parameters (‘current density parameters’) such as average value, RMS (root-mean-square) current densities etc.
It is often desirable to estimate the current density parameters on signal leads during the design of an integrated circuit. For example, the estimated values can be used to ensure that the current density parameters do not exceed corresponding pre-defined threshold values when the circuit is used later after fabrication. Such operation generally leads to reliable operation of integrated circuits in their intended lifetime, as is well known in the relevant arts.
Current density parameters are typically estimated in a design phase by performing a simulation (e.g., using SPICE program, well known in the relevant arts) based on a digital representation of the integrated circuit. In one prior approach, the simulated components include all the lower level components (transistors, etc.) of driver cell(s) and load cells along with the connected signal leads.
One advantage of such an approach is that the estimated values (for the current density parameters) closely represent the parameters that would be encountered when the integrated circuit is operational. However, one problem with the approach is that a substantial amount of computational resources (e.g., processor time, memory) may be required to determine the parameters of a signal on the signal lead. In addition, such an approach may require a substantial number of data inputs, which may not be always available. Accordingly, the corresponding solutions may be unacceptable at least in some environments.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.